EP0598038A1

EP0598038A1 - Cellulose acetoacetates.

Info

Publication number: EP0598038A1
Application number: EP92917835A
Authority: EP
Inventors: Kevin Joseph Edgar; William Williamson Blount Jr
Original assignee: Eastman Kodak Co
Current assignee: Eastman Chemical Co
Priority date: 1991-08-09
Filing date: 1992-07-30
Publication date: 1994-05-25
Anticipated expiration: 2012-07-30
Also published as: DE69218606D1; TW218384B; WO1993003063A1; CA2106189A1; DK0598038T3; US5360843A; ES2099276T3; GR3023538T3; JPH06510805A; EP0598038B1; US5292877A; ATE150768T1; DE69218606T2

Abstract

Water soluble cellulose acetoacetates prepared by contacting a cellulose material with diketene, an alkyl acetoacetate, 2,2,6-trimethyl-4H-1,3-dioxin-4-one or a mixture thereof in a solvent system comprising lithium chloride plus a carboxamide. Compositions containing the cellulose acetoacetates and, optionally, a crosslinking agent are useful for coatings applications.

Description

CELLULOSE ACETOACETATES

Field of Invention

This invention concerns novel cellulose aceto— acetates ("CAA"s) including some that are water soluble, as well as a process for production thereof and coating compositions prepared therefrom.

Background of the Invention Acetoacetylated polymers are of intense current interest. Incorporation of acetoacetate groups into polymers generally affords several benefits, including reduction of solution viscosity (valuable in coatings applications) and introduction of a handle (the aceto— acetate group) for ready polymer crosslinking. The crosslinking chemistry of the acetoacetate group is rich and growing. These attributes make acetoacetylated polymers of particular interest in thermoset coatings applications. Polymers with affinity for water are also currently of great interest. Water—soluble polymers can be used to change the rheology of aqueous solutions, and so find many industrial applications, for example in the food industry as thickeners, in the oilfield industry as suspension aids, in the pharmaceutical industry as excipients, and in the coatings industry as film formers.

Cellulose is a readily available, naturally occurring polymer, whose derivatives are highly valued in coatings applications as well as the other industrial applications cited above. It is clear, therefore, that the ability to efficiently acetoacetylate cellulose might afford products of commercial interest. In particular, if water—soluble products could be made in this way, materials of great interest in industry might resul .

There is relatively little literature on the aceto¬ acetylation of cellulose. P. J. Wiezevich and A. H. Gleason (U.S. Patent 2,103,505, 1937) taught a method of acetoacetylation with diketene (which they incorrectly called "cyclobutane 1,3—dione") which they applied to cotton linters in one of their examples. They claimed cellulose acetoacetate by reaction of diketene with cotton linters employing "an acid esterification catalyst", but gave no supporting details either the method or the product.

H. Staudinger and T. Eicher .Makromol. Chem., 1953, 10, 261—279) teach complete acetoacetylation of cellulose employing a heterogeneous system of regenerated cellulose in acetic acid with sodium acetate catalyst, and diketene as acetoacetylating reagent. They obtained a product with a degree of substitution ("DS") per anhydroglucose unit ("AGU") of 3.0, as measured by elemental analysis. The product was soluble in acetic acid and acetone, and insoluble in water.

V. H. Reblin expanded upon these results .Chimia. 1968, 22_., 230—233). He treated cotton with diketene, according to the method of Staudinger and Eicher. This gave a partially acetoacetylated cotton, still water insoluble, which was subjected to crosslinking with aliphatic dia ines. Reblin found that the crosslinking gave bis(enamine) linkages, and dramatically decreased the tensile strength of the cotton. The crosslinks could be hydrolyzed with dilute acids.

None of these prior art teachings allow direct, homogeneous acetoacetylation of cellulose to the desired DS. None of them give evidence of preparing a homogeneously substituted CAA with DS/AGϋ less than 3.0. Nothing known in the prior art teaches preparation of a water—soluble cellulose acetoacetate. Nothing^•known in the prior art teaches acetoacetylation of cellulose in the absence of acid or base catalysis.

Most of the known cellulose solvents are unsuitable for reactions in which cellulosic hydroxyls serve as nucleophiles. The solvent systems recently introduced by C. L. McCormick (U.S. Patent 4,278,790, 1981) and A. F. Turbak, A. El—Kafrawy, F. W. Snyder, Jr., and A. B. Auerbach (U.S. Patent 4,302,252, 1981) are exceptions in that they do permit certain such reactions. McCormick and Turbak et al. have taught that cellulose may be dissolved in solutions of lithium chloride in either N,N—dimethylacetamide or 1—methyl—2— pyrrolidinone. McCormick has further taught (U.S. Patent 4,278,790; Polymer. 1987, 28., 2317-2323) that electrophilic reagents may be added to these cellulose solutions to derivatize cellulose. McCormick has prepared cellulose acetate, methyl cellulose, cellulose carbamate, and other derivatives (but not CAA) in this way.

There is, therefore, a need for a process by which CAA of the desired degree of substitution may be prepared directly from cellulose. It is desirable that cellulose be reacted in solution, to assure homogeneous substitution along the polymer chains. The process should be economical and amenable to scale up to industrial production. It would be desirable to have available from this process a CAA of the correct composition, such that it would have good solubility in water.

Summary of the Invention

The present invention is directed to a synthesis process for preparing cellulose acetoacetate, said process comprising contacting in any order the following:

(i) a cellulose material, (ii) diketene, an alkyl acetoacetate, 2,2,6—tri ethyl— 4H—1,3—dioxin—4—one, or a mixture thereof,

(iii) a solubilizing amount of a solvent system comprising lithium chloride plus a carboxamide selected from the group consisting of 1—methyl—2— pyrrolidinone, N,N—dimethylacetamide, or a mixture thereof, and

(iv) optionally, a catalytic amount of pyridine,

NaOAc, Et₃N, a ine, mineral acid, or alkali or alkaline earth metal salt under conditions to promote formation of the desired cellulose acetoacetate. After the desired product is formed it is generally desirable to perform the optional additional step of insolubilizing the CAA by addition of an insolubilizing amount of a nonsolvent.

The present invention is also directed to cellulose acetoacetates having a DS/AGU of 0.1 to 2.9. Preferably the novel, water—soluble cellulose acetoacetates have a DS/AGU of 0.4 to l.l, more preferably 0.8 to 1.0.

The present invention is also directed to a coating composition comprising: (A) 0.5 to 50 percent, based on the weight of the total coating composition, of a water soluble cellulose acetoacetate, (B) 25 to 95 percent, based on the weight of the total coating composition, of water, and (C) 0 to 40 percent, based on the weight of the cellulose acetoacetate, of a crosslinking agent. The present invention is further directed to a process for preparing a coated substrate comprising contacting said substrate with a coating composition comprising: (A) 0.5 to 50 percent, based on the weight of the total coating composition, of water soluble cellulose acetoacetate,

(B) 25 to 95 percent, based on the weight of the total coating composition, of water, and

(C) 0 to 40 percent, based on the weight of the cellulose acetoacetate, of a crosslinking agent, followed by removing water and thermal curing.

Additionally, the present invention includes a coated substrate comprising a substrate having coated thereon a cured water soluble cellulose acetoacetate.

Detailed Description of the Invention

The unique ability of certain of the aceto— acetylated cellulose polymers of the invention to be completely solubilized by water makes them useful in low VOC (volatile organic content) coatings. Low VOC is becoming increasingly desirable because of environmental and regulatory considerations. By the term "water soluble" and derivative terms thereof it is meant that upon contacting the cellulose acetoacetate with an excess of water (a solubilizing amount) at 25°C, and optionally mixing, the cellulose acetoacetate becomes solubilized or dissolved, without the need for additional cosolvents or dispersing aids, at a level of at least 10 wt. percent, preferably at least 20 wt. percent.

The practice of the current invention allows for a wide variety of cellulose starting materials, temperatures, concentrations, nonsolvents, and reactant ratios. A wide variety of CAA's may be produced, depending on the conditions selected. The cellulose acetoacetates of the invention have the desired DS/AGU and comprise repeating units of the structure:

-° ⁾ wherein R, R' , and R' ' are selected separately from the group consisting of: hydrogen and acetoacetyl.

The CAA's of the invention typically have an intrinsic viscosity (IV) as measured in dimethyl— sulfoxide (DMSO) at a concentration of 0.25 g polymer/100 ml solvent at 25°C of 0.05 to 3.5, preferably 0.2 to 1.0. The weight average molecular weight (K..) as measured by gel permeation chromatography in 1—methyl—2— yrrolidinone using polystyrene standards is typically 40,000 to 1,000,000.

A wide variety of celluloses may be used for the process of the invention. It should be especially noted that the crystal structure of the cellulose starting material is irrelevant, since it will be destroyed when the cellulose is dissolved. This permits use of cellulose from low—price sources, which are not as useful in conventional heterogeneous cellulose reactions. The cellulose sources useful in our invention include hardwoods , softwoods, bacterial and microcrystalline cellulose.

The solvent system useful herein and as taught by McCormick must include lithium chloride plus a carboxamide. The carboxamide may be 1—methyl—2— pyrrolidinone, N,N—dimethylacetamide, or a mixture thereof. The ratios of carboxamide/cellulose and LiCl/cellulose may vary within a moderately wide range.

The acetoacetylating reagent may be either diketene, 2,2,6—trimethyl— H—1,3—dioxin—4—one, or an alkyl acetoacetate wherein the alkyl group is straight chain or branched and has 1 to 18 carbon atoms. As taught by J. S. Witzeman (Tet. Lett. , 1990, 31. 1401—1404) , tert—butyl acetoacetate is an especially suitable alkyl acetoacetate because it generates the reactive intermediate, acetylketene, at a high rate.

Catalysts are not necessary if the process of the current invention is carried out in the temperature range of 80—160°C as described below. Catalysts may be used to permit use of lower temperatures in the process. Such catalysts include (but are not limited to) amines (including pyridine, alkylpyridines, triethylamine, and 4—dimethylaminopyridine) , mineral acids (including sulfuric acid and hydrochloric acid) and alkali or alkaline earth metal salts (including sodium acetate, lithium chloride) .

In the synthesis process of the invention the molar ratio of component (i) :component (ii) is that amount that will result in the desired DS/AGU under the chosen reaction conditions. This mole ratio of component (i):component (ii) is typically 1:1 to 1:5. The amount of component (i) is typically 0.1 percent to 8 percent, preferably 3 percent to 5 percent, based on the weight of the carboxamide. The amount of lithium chloride is typically 100 percent to 300 percent, preferably 150 percent to 250 percent, based on the weight of component (i) .

Conditions suitable for the formation of CAA'ε can vary widely. The temperature for contacting the cellulose material (i.e., component (i) ) with the acetoacetylating reagent (i.e., component (ii)) in the solvent system can vary between 80—160°C, with 100—120°C most preferred, except in the case where a catalyst is used. When a catalyst is present, the temperature can range from —30—160°C, with 10—100°C preferred and 15—80°C most preferred. The addition time (contact time) can vary from 0.1—10 hours, with 1—2 hours most preferred. After the contact or addition time it is often desirable to further extend the total reaction period by holding the contacted components for a hold time at a certain hold temperature. The hold temperature after addition (i.e., after all of components (i) , (ii) and (iii) have been contacted) can vary from 80—160°C (—30—160°C in the catalyzed process) at a hold time of 0 to 10 hours, preferably 0.5 to 10 hours. Hold time and temperature can be used to adjust the molecular weight of the final product in the uncatalyzed process, and in some cases its solubility. Higher temperatures lead to lower molecular weights. For high molecular weight products, temperatures of 100—120°C are preferred. For low molecular weight products, temperatures of 140—160°C are preferred. Those of skill in the art readily recognize that reaction times and reaction temperatures employed are interdependent and thus can vary considerably.

The yield of CAA in the process of the invention is at least 80 percent, preferably at least 98 percent, said percentages being based on the theoretical maximum yield of CAA. Nonsolvents to be used in the isolation of the CAA can be any solvent in which the reaction solvents and by—products are miscible, but in which the CAA is insoluble. Preferred nonsolvents include methanol, ethanol, isopropyl alcohol, and acetone. An insolubilizing amount of nonsolvent is generally at least 900 percent, based on weight of nonsolvent per weight cellulose used. After insolubilizing the CAA with nonsolvent, it is typically desired to perform the additional optional step of separating the CAA from the nonsolvent, e.g., by filtration, drying, •decantation, washing, and the like, to result in substantially pure CAA.

The class of CAA prepared as taught herein and having the desirable property of being dissolved or dispersed in water without the need of added organic cosolvents or other dispersing aids can be formulated into croεslinkable coatings. Fully formulated, pigmented and catalyzed, water—borne CAA enamels are prepared by first adjusting the viscosity of a CAA/water solution to a Gardner-Holdt viscosity of Zl—Z3 [1000 to 3000 cP] (1 to 3 Pa.s) then mechanically dispersing a pigment, such as rutile titanium dioxide, until the desired fineness—of—dispersion is obtained.

Crosslinking resins, catalysts, rheological additives, anti—settling agents, tinting pigments, flexibilizing plasticizers and the like can be added to the CAA/water/pigment dispersion as needed during a final letdown to application viscosity. Of course, final viscosity requirements will vary with application and will be 100 cP (0.1 Pa.s) for air—atomized spraying to 1000 cP (1 Pa.s) for roller coating operations. Other procedures such as masterbatch preparation and the use of pre—dispersed pigments would also be acceptable. The coatings test procedures used in the description and examples of this invention are as follows: 1. Testing Coated Metal Specimens at 100 Percent

Relative Humidity — Cleveland humidity (ASTM Method D 2247) 2. Gardner-Holdt Bubble Viscosity (ASTM Method D 1545)

3. Film Thickness (General Electric Gage, Type B)

4. Film Hardness (Pencil Method)

5. Solvent resistance (methylethyl ketone (MEK) dynamic rub test) (see ASTM Method D 1308) 6. Staining Tests (ASTM Method D 1540) 7. Specular Gloss (ASTM Method D 523)

8. Hegmann Fineness—of—Dispersion (ASTM Method D 1210) As appreciated in the art, the exact components and properties of components desired for any given coating application can vary, and therefore, routine experi¬ mentation may be required to determine the optional components and proportions of components for a given application and desired properties.

Preferred crosslinking agents contain substituted melamine and urea resins or residues such as hexamethoxymethylmelamine, hexabutoxymethylmelamine, tetramethoxymeth lurea, or tetrapropoxymethylurea. Other useful crosslinking materials are amine terminated polyamides, polyoxyethylenes, polyoxypropylenes and the like. Particularly useful are an amino resin offered by American Cyanamid, CYMEL 303 (trademark) , and a polyamine available from Texaco, JEFFAMINE D230 (trademark) . The coating composition of the mixture preferably contains at least 0.1 percent crosslinking agent (component (C) ) , preferably 1 percent to 35 percent crosslinking agent (component (C)) , and more preferably 2 to 25 percent, said percentages being based on the weight of the CAA. It is particularly preferred that the crosslinking agent is a melamine resin, a urea resin, an amino resin, or a mixture thereof and is present in an amount of 0.5 to 40 percent, based on the weight of the CAA. In the coating composition a preferred amount of component (A) is 2.5 to 30 percent, more preferred is 5 to 25 percent; and a preferred amount of component (B) is 30 to 80 percent, more preferred is 40 to 60 percent, said percentages being based on the total weight of the coating composition.

The coating composition optionally contains up to 70 weight percent based on the weight of coating binder, that is component (A) plus component (C) , of one or more additional coating additives.

A preferred amount of coating additives is 1 to 30 percent. Examples of such coating additives include flow control additives such as siliconeε, fluorocarbons, or cellulosics; coalescing solvents such as diethylene glycol monobutyl ether, trimethylpentanediol monoisobutyrate, or ethylene glycol monooctyl ether; strong acid catalysts such as p—toluenesulfonic acid, trichloroacetic acid, or trifluoromethanesulfonic acid; pigments such as titanium dioxide, barytes, clay, or calcium carbonate; colorants such as phthalocyanine blue, molybdate orange, or carbon black; biocides such as tin compounds (e.g., tributyltin oxide), quaternary ammonium compounds, or iodine compounds; thickeners such as carboxymethyl cellulose, hydroxypropyl methyl cellulose, ethyl hydroxyethyl cellulose, guar gum and the like.

The Gardner—Holdt viscosity of the coating composition is preferably T to Z3; more preferably W to

Zl. These viscosity values permit application by spraying and/or wire—rod drawdowns (which simulate a roller coating operation) as practiced in Examples 6—9 hereof. The coating composition can be prepared by the techniques described herein and/or by techniques known in the art, e.g., as disclosed in U.S. Patents 4,698,391, 4,737,551, and 3,345,313, the disclosures of which are incorporated herein by reference in their entirety.

The coating composition can be applied onto a substrate and crosslinked using techniques known in the art; e.g., by spray—applying 3 to 4 mils of wet coating and baking in a 150°C forced air oven for 30 minutes, by similarly preparing and baking at a lower temperature of 60°C for one hour, or in some cases by curing at ambient temperature for 2 to 24 hours.

The substrate can be any common substrate such as paper, polymer films such as polyethylene or poly— propylene, metals such as aluminum, steel, galvanized steel, glass, urethane elastomers, primed (painted) substrates, and the like.

After the coating composition is coated onto a substrate and cured (i.e., crosslinked) such a cured coating has many desirable properties such as good pencil hardness, good gloss, good humidity resistance, and good MEK double rub solvent resistance.

Preferred pencil hardness (mar/cut) is B to 4H; more preferred is at least F; preferred gloss at 60°C is 40 percent to 100 percent, more preferred is above 60 percent; preferred solvent rub resistance is at least 200, more preferred is at least 250; preferred humidity resistance (100 hours at 60°C) is 70 to 100 gloss retention, more preferred is 88—100 percent gloss retention.

EXAMPLES In the following examples, the cellulose and carboxamide solvent used were loaded into a 500 mL, three—necked round bottom flask equipped with mechanical stirrer, thermometer, nitrogen inlet, and reflux condenser. The slurry was heated to 100°C under nitrogen, then the amount of LiCl used was added all at once. The slurry was heated to 150°C, then the heat was removed and the mixture was allowed to cool slowly to room temperature. The cellulose dissolved during the cooling period, usually within 3 hours of the time when the heat was removed. The straw—colored, highly viscoelastic solution was heated to the addition temperature, at which point the indicated amount of the indicated acetoacetylation reagent was added over the indicated time period. The resulting solution was held at the addition temperature for the indicated hold time, then was cooled to room temperature. The product was isolated by precipitation with methanol and purified by washing with methanol. The product was dried for analysis at 40-60°C under vacuum. The results in the examples indicate yields of isolated, well—characterized products. The products typically were characterized by intrinsic viscosity, gel permeation chromatography

(1—methyl—2—pyrrolidinone solvent, polystyrene reference standard) , infrared spectroscopy, 1H and 13C NMR spectroscopy, and other methods familiar to one well versed in the art. The degree of substitution was determined by digestion with n— utyl alcohol at reflux, followed by measurement of n—butyl acetoacetate by gas chromatography vs. an internal standard (see Example 10) , and/or by proton NMR.

Examples 10—13 provide crosslinkable enamel formulations prepared from cellulose acetoacetate polymer. The CAA materials are treated with a methylated melamine resin (hexamethoxymelamine) for baking systems (Examples 10 and 12) and with amine— functional polyethers to effect room temperature ena ine cure (Examples 11 and 13) . Properties of these novel systems are given in Table 1.

EXAMPLE 1

Reagents set forth below were subjected to the standard procedure described above under the indicated reaction conditions. The results, in terms of identity and yield of the desired cellulose acetoacetate, and key analyses of the product, are also set forth below. Starting Cellulose Natchez HVX (hardwood cellulose pulp, available from International Paper in Natchez, Mississippi)

Weight (g) 8.00

Solvent N,N—Dimethylacetamide (DMAC) Volume (mL) 1275

LiCl Weight (g) 120

Addition Temperature 110°C

Acetoacetylation Reagent tert—Butyl Acetoacetate

(tBAA)

Weight (g) 140.52

Addition Time (h)

Hold Time (h)

CAA Yield 67.70 g, 97.9 percent of theory

Key Analyses Degree of substitution (DS) 0.85, IV (DMSO) 2.05, M_n 91,000, M_w 265,000, K_∑ 627,000, solubility in H₂0 >10 percent

This example differs from the standard procedure in that a 3L flask was used.

This example demonstrates that acetoacetylation of cellulose in solution in LiCl/DMAC, using tBAA, can afford water—soluble CAA.

EXAMPLE 2

Reagents set forth below were subjected to the standard procedure described above under the indicated reaction conditions. The results, in terms of identity and yield of the desired cellulose acetoacetate, and key analyses of the product, are also set forth below. Starting Cellulose Microcrystalline Cellulose

(Avicel PH-105) Weight (g) 40

CAA Yield 48.02 g, 84.8 percent of theory

Key Analyses DS 0.80, IV (DMSO) 1.10, M.n 45,000, M_w 132,000, M 392,000, water solubility >20 percent

This example demonstrates that microcrystalline cellulose is a suitable substrate for the reaction, that it affords highly water—soluble CAA under the proper conditions, and that LiCl/NMP is a suitable solvent for the reaction.

EXAMPLE 3

Reagents set forth below were subjected to the standard procedure described above under the indicated reaction conditions. The results, in terms of identity and yield of the desired cellulose acetoacetate, and key analyses of the product, are also set forth below. Starting Cellulose Natchez HVX Weight (g) 8.00

Solvent NMP Volume (mL) 195

LiCl Weight (g) 20

Addition Temperature 110°C

Acetoacetylation Reagent Diketene Weight (g) 12.44

Addition Time (h) 1.5

Hold Time (h) 0.75

CAA Yield 7.74 g, 53.3 percent of theory

Key Analyses DS 1.57, M_n 62,000, _^_ 282,000, M 777,000, insoluble m water, soluble in DMSO or DMF

This example demonstrates that diketene is a suitable reagent for the solution acetoacetylation of cellulose and that higher DS, water—insoluble materials are available by proper variation of this technique.

EXAMPLE 4

Reagents set forth below were subjected to the standard procedure described above under the indicated reaction conditions. The results, in terms of identity and yield of the desired cellulose acetoacetate, and key analyses of the product, are also set forth below.

CAA Yield 12.32 g, 98.7 percent of theory

Key Analyses DS 1.08, insoluble in water, soluble in DMSO or DMF

This example differs from the standard procedure in that 3 mL of pyridine was added prior to diketene addition (but subsequent to cellulose dissolution) as an acylation catalyst.

This example demonstrates that acetoacetylation can be carried out at near—ambient temperature if a pyridine catalyst is employed.

EXAMPLE 5

Reagents set forth below were subjected to the standard procedure described above under the indicated reaction conditions. The results, in terms of identity and yield of the desired cellulose acetoacetate, and key analyses of the product, are also set forth below. Starting Cellulose Natchez HVX Weight (g) 48

Solvent DMAC Volume (mL) 1275

LiCl Weight (g) 120

Addition Temperature 110°C

Acetoacetylation Reagent tBAA Weight (g) 140.52

Addition Time (h) 4

Hold Time (h) 2

CAA Yield 49.72 g, 83.3 percent of theory

Key Analyses DS 0.47, IV (DMSO) 0.53, Mn. 22,000, M_y 53,000, M 120,000, water solubility >20 percent

This example differs from the standard procedure in that after the conclusion of the hold time at 110°C, the solution was heated to 150°C for 30 minutes with the intention of reducing molecular weight of the polymer. The solution then was cooled to room temperature and the product isolated as in the standard procedure.

This example demonstrates that a high molecular weight cellulose starting material can be used to generate relatively low molecular weight CAA which has very high water solubility, by the simple expedient of a brief period of heating to 150°C to reduce somewhat the polymer molecular weight.

EXAMPLE 6

CAA Yield 11.13 g, 91.6 percent of theory

Key Analyses DS 0.96, IV (DMSO) 1.45, Mn 186,000, M_w 623,000, M_z 1,460,000, soluble in NMP, N,N—dimethylformamide and DMSO

This example differs from the standard procedure in that a catalyst was used (added just before diketene at ambient temperature) .

The example demonstrates that, in the presence of pyridine as catalyst, the acetoacetylation proceeds in NMP rapidly even at room temperature. EXAMPLE 7

CAA Yield 7.33 g, 90.0 percent of theory

Key Analyses DS 0.18, swells in water, DMF, and DMSO

This example differs from the standard procedure in that a catalyst was used (added just before diketene at ambient temperature) . Also, excess sodium bicarbonate was added at the end of the hold time to neutralize the catalyst.

The example demonstrates that, in the presence of sulfuric acid as catalyst, the acetoacetylation proceeds even at room temperature. EXAMPLE 8

Starting Cellulose Natchez HVX Weight (g) 5.68

Solvent NMP Volume (mL) 133

LiCl Weight (g) 14.2

Catalyst Sodium Acetate Weight (g) 0.80

Addition Temperature 60-70°C

Acetoacetylation Reagent Diketene Weight (g) 11.8

Addition Time (h) 0.33

Hold Time (h) 2.7

Hold Temperature 60-68°C

CAA Yield 6.66 g, 101.0 percent of theory

Key Analyses DS 0.31, swells in water, DMSO, and DMF

The example demonstrates that, in the presence of sodium acetate as catalyst, the acetoacetylation proceeds rapidly even at 60—70°C. EXAMPLE 9

Starting Cellulose Natchez HVX Weight (g) 8.00

Solvent NMP Volume (mL) 187

LiCl Weight (g) 20.0

Catalyst None

Addition Temperature 24-25°C

Acetoacetylation Reagent Diketene Weight (g) 16.6

Addition Time (h) 0.08

Hold Time (h) 25

Hold Temperature 24-28°C

CAA Yield 14.79 g

Key Analyses DS 0.80, soluble in DMF, highly swollen in DMSO

This example demonstrates that, even without an added catalyst, the acetoacetylation proceeds slowly at room temperature, suggesting that lithium chloride is itself a catalyst for the reaction.

EXAMPLE 10

The water soluble cellulose acetoacetate of Example 1 (100 g) was dissolved in water (1200 g) to give a clear solution having a Brookfield viscosity of 470 cP (0.47 Pa.s). DuPont's R900 rutile titanium dioxide (100 g) was added and dispersed in an IKA Ultra Turrax T50 disperser to a Hegman Fineness or dispersion value of 7. This product, referred to as "Grind A" was used to make the following fully formulated melamine crosslinked enamel:

Inσredient Liquid Solid

Grind A 100.0 g

CAA ^■7 g

Ti0₂ 7 g Cyanamid's Cymel 303 3.3 g g p—Toluenesulfonic .14 g 06 g acid, 40 percent 3M Company FC430 .10 g 02 g

Flow Aid, 20 percent

Pigment/Binder 41.2/58.8 Resin/Crosslinker 70/30 Solvent Water Percent Solids 18.0

This white industrial baking enamel was applied to 20 gauge iron phosphate pre—treated steel test panels, cured at 150°C for 30 minutes to a dry film thickness of 0.25 mils and subjected to the tests shown in Table 1 below.

EXAMPLE 11

The cellulose acetoacetate/TiO- dispersion, Grind A, of Example 10 was used to prepare the following low—temperature—cure enamine crosslinked enamel formulation: Ingredient Liguid Solid

Grind A 100.0 g

CAA 7.7 g Ti0₂ 7.7 g

Texaco's Jeffamine D230 2.3 g 2.3 g

Pigment/Binder : 43.5/56.5

Resin/Crosslinker : 77/23 Solvent : Water

Percent Solids : 17.3

This coating was applied to 20 gauge iron phosphate pre— reated steel test panels, force—dried at 60°C for one hour, ambient cured for an additional 23 hours at room temperature, then subjected to the tests shown in Table 1 below.

EXAMPLE 12

The water soluble cellulose acetoacetate of Example 2 (100 g) was dissolved in water (1000 g) to give a clear solution having a Brookfield viscosity of 60 cP (0.06 Pa.s). DuPont's R900 rutile titanium dioxide (100 g) was added and dispersed in a IKA Ultra Turrax T50 disperser to a Hegman Fineness or dispersion value of 7. This product, referred to as "Grind B", was used to make the following fully formulated melamine crosslinked enamel:

Ingredient Liquid Solid

Grind B 100.0 g

CAA 9, i g

Ti0₂ 9, 1 g Cyanamid's Cymel 303 3.9 g 3, 9 g p—Toluenesulfonic .16 g 06 g acid, 40 percent 3M Company FC430 12 g 02 g

Flow Aid, 20 percent

Pigment/Binder 41.2/58, Resin/Crosslinker 70/30 Solvent Water Percent Solids 21.3

This white industrial baking enamel was applied to 20 gauge iron phosphate pre—treated steel test panels, cured at 150°C for 10 minutes to a dry film thickness of 0.25 mils and subjected to the tests shown in Table 1 below.

EXAMPLE 13

The cellulose acetoacetate/Ti0₂ dispersion, Grind B, of Example 12 was used to prepare the following low-temperature—cure enamine crosslinked white enamel formulation containing phosphoric acid to aid adhesion to steel:

Ingredient Liquid Solid

Grind B 100.0 g CAA 9, i g τio₂ 9. i g Texaco's Jeffamine D230 2.7 g 2, 7 g Phosphoric Acid 0.05 g

Pigment/Binder 43.5/56.5 Resin/Crosslinker 77/23 Solvent Water Percent Solids 20.3 This coating was applied to 20 gauge iron phosphate pre—treated steel test panels, force—dried at 60°C for one hour, ambient cured for an additional 23 hours at room temperature, then subjected to the tests shown in Table 1 below.

EXAMPLE 14

Cellulose acetoacetate samples were analyzed by taking advantage of the fact that, ' at high temperature, they thermally decompose into cellulose and acetylketene at a moderate rate. Trapping of the acetylketene by a primary alcohol which will afford a volatile acetoacetate ester permits analysis of the produced ester by gas chromatography (GC) . A sample of the ester from Example 1 (0.3000 g) was weighed into a 120 mL microwave vessel. Five mL of internal standard solution (1 mL of 1—methylnaphthalene in 250 mL n—butanol) was added to the vessel, then 30 mL n—butanol was added. A total of 5 such vessels (if less than 5 samples were being analyzed, the remaining vessels were charged with 35 mL n—butanol blanks) were placed in a rotating turntable in an industrial microwave oven (CEM MDS—8ID) . The oven was set to 55 percent power and turned on for 60 minutes with the turntable rotating. In another experiment with an equal volume of neat n— utanol in each vessel it was found that the temperature in each vessel stabilized at 160°C. At the end of this time the samples were cooled to room temperature and the supernatant liquid was analyzed by GC. Standard GC techniques permitted determination of the weight of n—butyl acetoacetate generated per gram of sample. This allowed simple calculation of the moles of acetoacetyl per gram of sample, thus the weight percent acetoacetyl, and thus the degree of substitution. This analysis has been confirmed by proton nuclear magnetic resonance spectroscopy.

Table 1 - Performance of Cellulose Acetoacetate-Based Coatings

Property

Cured Film Thickness

Specular Gloss, 60°/20°

Pencil Hardness

Solvent Resistance, MEK, rubs

Iodine Stain Resistance, 5 minutes (1-5, 5 best)

Direct Impact Resistance, in lbs. 40 60 10 40

Humidity Resistance Blisters None Not None Not Gloss Retention, percent 90 Recommended 90 Recommended

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. Moreover, all patents, patent applications (published or unpublished, foreign or domestic) , literature references or other publications noted above are incorporated herein by reference for any disclosure pertinent to the practice of this invention.

Claims

We Claim:

1, A process for preparing cellulose acetoacetate, said process comprising contacting in any order the following:

(i) a cellulose material, (ii) diketene, an alkyl acetoacetate, 2,2,6—trimethyl—4H—1,3— ioxin—4—one, or a mixture thereof, (iii) a solubilizing amount of a solvent system comprising lithium chloride plus a carboxamide selected from the group consisting of 1—methyl—2—pyrrolidinone,

N,N—dimethylacetamide, or a mixture thereof, and (iv) optionally, a catalytic amount of pyridine, NaOAc, Et₃N, amine, mineral acid, or alkali or alkaline earth metal salt under conditions to promote formation of the desired cellulose acetoacetate having a DS/AGU of 0.1 to 2.9.

2. The process of Claim 1 wherein the amount of cellulose material is 0.1 percent to 8 percent, based on the weight of said carboxamide, and the amount of lithium chloride is 100 percent to 300 percent, based on the weight of said cellulose material.

3. The process of Claim 1 wherein the amount of cellulose material is 3 percent to 5 percent, based on the weight of said carboxamide, and the amount of lithium chloride is 150 percent to 250 percent, based on the weight of said cellulose material.

4. The process of Claim 1 wherein the DS/AGU of the cellulose acetoacetate is 0.1 to 2.9.

5. The process of Claim 1 wherein the DS/AGU of the cellulose acetoacetate is 0.4 to 1.1.

6. The process of Claim 1 carried out at a temperature between 80°C and 160°C.

7. The process of Claim 1 having an addition time of 0.1 to 10 hours and a hold time of 0 to 10 hours.

8. The process of Claim 1 wherein said amine is pyridine.

9. The process of Claim 1 wherein said mineral acid is sulfuric acid.

10. The process of Claim 1 wherein said salt is lithium chloride or sodium acetate.

11. The process of Claim 1 carried out at a temperature between —30°C and 160°C in the presence of said catalyst.

12. The process of Claim 11 carried out at a temperature between 10° and 100°C.

13. The process of Claim 11 carried out at a temperature between 15° and 80°.

14. The process of Claim 7 wherein the addition time is 1 to 2 hours, the temperature during the addition time is 100°C to 120°C, the hold time is 0.5 to 10 hours, and the temperature during the hold time is 100°C to 120°C.

15. The process of Claim 14 wherein the temperature during the hold time is 140°C to 160°C.

16. The process of Claim 1 including the additional step of insolubilizing the cellulose acetoacetate by addition of an insolubilizing amount of a nonsolvent.

17. The process of Claim 16 including separating the insolubilized cellulose acetoacetate.

18. The process of Claim 16 wherein said nonsolvent is methanol, ethanol, isopropyl alcohol, acetone, or a mixture thereof.

19. A water soluble cellulose acetoacetate having a DS/AGU of 0.4 to 1.1.

20. The water soluble cellulose acetoacetate of Claim 19 having a DS/AGU of 0.8 to 1.0.

21. A coating composition comprising:

(A) 0.5 to 50 percent, based on the weight of the total coating composition, of a water soluble cellulose acetoacetate having a DS/AGU of 0.01 to 1.9,

(B) 25 to 95 percent, based on the weight of the total coating composition, of water, and (C) 0 to 40 percent, based on the weight of the cellulose acetoacetate, of a crosslinking agent.

22. The coating composition of Claim 21 wherein the amount of component (A) is 2.5 to 30 percent, the amount of component (B) is 30 to 80 percent, and the amount of component (C) is 1 to 35 percent.

23. The coating composition of Claim 21 wherein the amount of component (A) is 5 to 25 percent, the amount of component (B) is 40 to 60 percent, and the amount of component (C) is 2 to 25 percent.

24. The coating composition of Claim 23 wherein the amount of component (C) is 3 to 18 percent.

25. The coating composition of Claim 21 wherein said crosslinking agent is present in an amount of 0.5 to 40 percent and is a melamine resin, a urea resin, an amine—containing resin or a mixture thereof.

26. The coating composition of Claim 21 wherein said crosslinking agent is hexamethoxymethylmelamine, hexabutoxymethylmelamine, tetramethoxymethylurea, tetrapropoxymethylurea, an amine terminated polyamide, an amine terminated polyoxyethylene, an amine terminated polyoxypropylene, or a mixture thereof.

27. The coating composition of Claim 21 additionally containing up to 70 percent, based on the weight of the cellulose acetoacetate, of at least one additional coating additive.

28. The coating composition of Claim 21 additionally containing 1 to 30 percent, based on the weight of the cellulose acetoacetate, of at least one additional coating additive.

29. The coating composition of Claim 28 wherein said additional coating additive is a flow control additive, a coalescing solvent, a strong acid, a pigment, a dye, a biocide, or a thickener.

30. The coating composition of Claim 29 wherein said flow control additive is a silicone, a fluoro— carbon, or a different cellulose ester; said coalescing solvent is diethylene glycol monobutyl ether, trimethylpentanediol monoisobutyrate, or ethylene glycol monooctyl ether; said strong acid catalyst is p—toluenesulfonic acid, trichloroacetic acid, or trifluoromethanesulfonic acid; said pigment is titanium dioxide, a baryte, a clay, or calcium carbonate; said dye is phthalocyanine blue, molybdate orange or carbon black; said biocide is a tin compound, a quaternary ammonium compound, or an iodine compound; and said thickener is carboxy— methyl cellulose, hydroxypropyl methyl cellulose, ethyl hydroxyethyl cellulose, or guar gum.

31. The coating composition of Claim 21 having a Gardner-Holdt viscosity of T to Z3.

32. The coating composition of Claim 30 having a Gardner-Holdt viscosity of W to Zl.

33. A process for preparing a coated substrate comprising contacting said substrate with a coating composition comprising: (A) 0.5 to 50 percent, based on the weight of the total coating composition, of water soluble cellulose acetoacetate having a DS/AGU Of 0.01 to 1.9, (B) 25 to 95 percent, based on the weight of the total coating composition, of water, and

34. A coated substrate comprising a substrate having coated thereon a cured water soluble cellulose acetoacetate.

35. The coated substrate of Claim 34 wherein said substrate is paper, a polymer film, a metal, glass, or a urethane elastomer.

36. The coated substrate of Claim 35 wherein the substrate is primed.

37. The coated substrate of Claim 34 having a pencil hardness of B to 4H, a gloss at 60°C of 40 percent to 100 percent, a solvent rub resistance of at least 200, a humidity resistance at 60°C for 100 hours of 70 percent to 100 percent gloss retention.

38. The coated substrate of Claim 34 having a pencil hardness of at least F, a gloss at 60°C of 60 percent to 100 percent, a solvent rub resistance of at least 250, a humidity resistance at 60°C for 100 hours of 88 percent to 100 percent gloss retention.